The differentiation of malignant cytotrophoblasts into syncytiotrophoblasts will be studied in cultured human choriocarcinoma (BeWo), using methotrexate as a differentiation inducer. Time-lapse cinematography, cytological chromosome techniques, flow microfluorimetry and electron microscopy will be used in the analysis of the origin and reproductive potential of giant multinucleated syncytiotrophoblast-like cells of choriocarcinoma. Tissue culture techniques will be used to evaluate the role of multinucleated giant cells in viability enhancement and clonal diversification of the tumor cell population. Biochemical techniques and electron microscopy will be used to investigate differentiative changes in cell membrane lipids, cell surface glycosaminoglycans and lectin binding sites, and to study their regulation. Changes in cell adhesivity will be assayed during cyto-differentiation and the biochemical basis for these changes will be investigated. These studies will contribute to an understanding of the physiopathology of choriocarcinoma.